Automated analysis of biological specimens requires a high degree of repeatability and accuracy from the motion systems that position specimens in the instrument. Repeatability and accuracy errors can decrease throughput and, in the worst case, cause low prevalence data to be missed. Therefore, it is critical that motion systems employed in automated biological analysis machines perform above or beyond the engineered limits of the design.
For automated biological analysis applications, such as for Pap smear analysis, repeatability of movement of a microscope slide stage in the X,Y plane, or horizontal plane, is extremely important. In such systems prioritized images may be selected under low power magnification and are relocated under high power magnification for review. In one example of an automated biological analysis system as manufactured by NeoPath, Inc. of Bellevue, Wash. a low power 4.times. field of view is divided into a 5.times.5 matrix of high power 20.times. fields. Each 4.times. subfield (or 20.times. field) is analyzed for further review. If the results dictate further inspection, the system reviews the subfield with the 20.times. magnification. Thus, stage repeatability becomes most critical when an object of interest in a 4.times. subfield lies near the subfield boundary. In such a case, poor XY stage repeatability may cause the high power 20.times. review to miss a suspect object. Therefore, it is one motive of the present invention to provide an X,Y repeatability test. As contemplated by the present invention, an X,Y repeatability test is conducted to verify that stage performance meets engineered limits.
The method of the present invention ensures that priority fields of the low power scan are appropriately positioned under a high power objective for image collection and evaluation. The invention provides a process and apparatus suitable for characterizing lateral repeatability of the X-Y stage, the longitudinal repeatability of the Z stage, the cross coupling of motion in the Z direction from the X-Y stage, the repeatability of the microscope objective turret, the mechanical centration of optical paths and the parfocality of optical paths. This process involves moving to a rough location, performing focus pans to determine the best focus and searching for a known object to register coordinate locations, processing those locations to determine the repeatability and accuracy of the motion system. Further, a means of evaluating these parameters is disclosed by which the automated cytology instrument will validate or invalidate data taken since the last position integrity check.
In a presently preferred embodiment of the invention, the camera system disclosed herein is used in a system for analyzing cervical pap smears, such as that shown and disclosed in U.S. patent application Ser. No. 07/838,064, entitled "Method For Identifying Normal Biomedical Specimens", by Alan C. Nelson, et al., filed Feb. 18, 1992; U.S. patent application Ser. No. 07/838,395, entitled "Method For Identifying Objects Using Data Processing Techniques", by S. James Lee, et al., filed Feb. 18, 1992; U.S. patent application Ser. No. 07/838,070, now U.S. Pat. No. 5,315,700, entitled "Method And Apparatus For Rapidly Processing Data Sequences", by Richard S. Johnston, et al., filed Feb. 18, 1992; U.S. Patent Application Ser. No. 07/838,065, filed February 18, 1992, entitled "Method and Apparatus for Dynamic Correction of Microscopic Image Signals" by Jon W. Hayenga, et al.; and U.S. patent application attorney's docket No. 9/1799, filed Sep. 7, 1994 entitled "Method and Apparatus for Rapid Capture of Focused Microscopic Images" to Hayenga, et al., which is a continuation-in-part of application Ser. No. 07/838,063 filed on Feb. 18, 1992 the disclosures of which are incorporated herein, in their entirety, by the foregoing references thereto.